A wireless cellular telephony system will comprise a number of cells, each of which can accommodate a number of user terminals, UEs. The system will also comprise a function via which the traffic to and from the UEs in a cell is routed, a function which in a WCDMA system is known as the NodeB, sometimes also referred to as the Radio Base Station, RBS, of the cell.
A WCDMA system also comprises a function for the control of the NodeBs, a so called Radio Network Controller, RNC, a function which also carries out a certain degree of control of the UEs in a cell whose NodeB it controls. Each cell with its NodeB, and the UEs in that cell, will thus be tied to, and controlled by, a particular RNC in the system. The RNC of a cell maintains a list of cells which are in the vicinity of the cell in question. This list is usually known as the Neighbour cell list.
A UE of a WCDMA system can be in communication with more than one cell, or rather, the NodeB of that cell, at a time. The cells that the UE is in communication with at the moment are known as the Active Set of that UE. The RNC which controls a UE keeps a list of the cells of the Active Set of the UE.
A UE in a cell in a WCDMA system listens for transmissions from NodeBs of other cells, and reports such transmission to its RNC via the NodeB of the cell. If transmissions from a NodeB of a cell in the Neighbor list of the UE's cell are detected and subsequently reported to the RNC of the UE, the RNC can add that cell to the UE's AS. However, if transmissions from a NodeB of a cell which is not included in the Neighbor cell list of the UE's cell are detected by a UE, those cells can not be identified.
To have correct neighbour cell lists is important for a number of reasons, one of them being that “missing” neighbours will cause dropped calls and interference in the network. In present systems, a neighbour cell list for a typical WCDMA cell will contain approximately 15-20 neighbour cells, all of which must be identified and defined manually.
As can be understood, to define and maintain proper and correct neighbour cell lists is a necessary but large task for operators of WCDMA systems, in particular in a system which is expanding, and in which many new cells are added.